1. FIELD OF THE INVENTION
The present invention relates to a process for the control and adjustment of the flow of a viscous liquid in an apparatus which includes an applicator device.
2. THE PRIOR ART
In industry, automatic machines such as robots are used, among other things, for the automatic application of a seam of viscous liquid onto given tracks. The viscous liquid can be, for example, an adhesive, a sealing compound or a plastic substance. A specific example is the application by a controlled robot of an adhesive along a given track on a workpiece. This process occurs, for example, in the automobile industry for the application of an adhesive or a sealing compound on the inside of the outer sheet metal section of car doors, to which then the inner sheet metal section of the door is glued.
This technique requires that the applied seam have a desired thickness, i.e., that a desired amount of the viscous liquid is applied per unit length of the track. The amount sprayed or applied during a certain time unit is called the flow. Thus, the flow coming out of the applicator device has to be at a certain ratio to the frequent changes, during one operational cycle, of the track speed of the robot.
To execute the above process it is known to supply the applicator device, which is guided by the robot arm, with the viscous liquid through a flexible hose, the hose being connected to a cylinder filled with the viscous liquid, a piston in the cylinder expressing the liquid from the cylinder by applying a constant force thereto. The flow of the liquid can be changed by adjusting this force. However, in this known process the flow of the liquid can deviate from the set value because of varying viscosity, resulting from changes in the temperature, and from deterioration (obstruction) of the nozzle opening of the applicator device.
In order to adjust the thickness of the liquid seam, it is also known to construct the drive for the piston in the noted cylinder in such a manner that the piston operates independently of the resistance to be overcome and at an adjustable constant speed. In this process, the applicator device works with a constant nozzle opening. However, there is no means for checking that the applied amount per time unit conforms to the set value. A change is only possible by adjusting the speed of the piston, and this adjustment is subjected to a large time constant. When changing from one phase to the next within an operational cycle the speed and/or the amount of the viscous liquid to be applied per unit length is changed, so that at that time the flow of liquid has to be adjusted. At this point the high viscosity and thus inertia of the adhesive proves to be a disadvantage. For the transition from one to the next track section there is only a relatively short amount of time available, and within this time the required flow change has to be made. In addition, the pressure changes appear unfavorably in the viscous liquid, on the one hand, because the viscous liquid has a significant compressibility, and, on the other hand, because the supply hoses expand during high operational pressures of between 100 and 200 bar and shrink when the pressure is lowered. This results in variations in the amount of viscous liquid applied per unit length in the form of transient processes. Though it would be possible to largely eliminate the last noted effect by installing the piston cylinder arrangement on the robot hand, the weight of the robot arm, designed for rapid motions, would increase considerably, and this would result in a disadvantageous influence on the applicator speed.